Evaluation de l’effet antioxydant et détermination structurale de métabolites secondaires de Volutaria lippii syn. Centaurea lippii (Asteraceae).

Abstract

This work concerns the study of the species Volutaria lippii syn. Centaurea lippii, belonging to the Asteraceae family; a plant of the Algerian flora which has been the subject of very few previous studies. Our work began with the maceration of the aerial parts (leaves and flowers) in 70% methanol, followed by filtration, concentration and dilution with distilled water. The solution obtained was subjected to successive extractions with solvents of increasing polarity to give the chloroform, ethyl acetate and n-butanol extracts, whose polyphenols and total flavonoids were quantified by colorimetric methods. These tests showed that the ethyl acetate extract has the highest content followed by the n-butanol extract. Secondly we proceeded to the evaluation of their antioxidant activity by the scavenging tests of the DPPH radical and the cation radical ABTS, the bleaching test of β-carotene and finally the test of cupric reducing antioxidant capacity (CUPRAC). The best result was obtained for the ethyl acetate extract followed by the n-butanol extract. The results of the quantitative analyses and the evaluation of the antioxidant activity of these extracts, encouraged us to proceed with the fractionation of the ethyl acetate and nbutanol extracts, this step was carried out on columns of silica gel 60. The fractions obtained were purified by chromatography on preparative silica gel plates and by semi-preparative HPLC in reverse phase equipped with UV-Vis and IR detectors. These experiments allowed us to isolate and purify twenty compounds. The structural determination of fourteen of the isolated and purified compounds was carried out by combining spectroscopic analysis techniques: 1H NMR, HSQC, HMBC and COSY, mass spectrometry and UV-Vis spectrophotometry. These compounds were:  Six sesquiterpene lactones including a new one that we describe for the first time in the literature: 3-hydroxy-11β,13-dihydrodehydrocostuslactone 8α-O-(6'-acetyl-β- glucopyranoside), three described for the first time for the species Volutaria lippii: (3β-hydroxy-11β,13-dihydrodehydrocostuslactone 8α-O-β-glucopyranoside,desacylcynaropicrin, deacylcynaropicrin 8-O-[(S)-3-hydroxy-2-methylpropionate]) and two already reported for this species, 11β,13-dihydrodeacylcynaropicrin and cynaropicrin. Two megastigmanes: described for the first time for the species Volutaria lippii, (6R,9R)-3-oxo--ionol-β-D-glucopyranoside and lippianoside E  Two flavonoids: one of which is described for the first time for the species Volutaria lippii (apigenin-7-O-glucoside) and luteolin  Two phenolic acids: described for the first time for the species Volutaria lippii, caffeic acid and ferulic acid  A glucosylated alkene: described for the first time for the species Volutaria lippii, (Z)-3- hexenyl O-β-D-glucopyranoside)  A glucosylated aromatic derivative: described for the first time for the species Volutaria lippii, phenyl-methyl-O-β-D-Glucopyranoside